Impact of Atrazine on Periphyton in Freshwater Enclosures and Some Ecological Consequences

Abstract

The herbicide atrazine inhibited production of periphyton within limnocorrals (in situ aquatic enclosures) and altered the composition of the periphyton community. On two occasions, 6 wk apart, theree limnocorrals were treated with a surface application of atrazine equivalent to a nominal enclosure concentration of 100 .mu.g .cntdot. L-1. During the first atrazine pulse, the Cyanophyta disappeared and organic matter decreased to values significantly less than those within three control enclosures. Within 3 wk of the second atrazine application, a 36-67% reduction in organic matter, chlorophyll, and algal biomass and a significant decrease in the rate of carbon assimilation were evident. These events coincided with a decrease in number of certain Chlorophyta species, although other Chlorophyta species increased in number. The Bacillariophyceae maintained biomass levels greater than those in the controls for 9 wk after the second atrazine application. Total limnocorral periphyton production was greater than that of the phytoplankton after 5-10 wk of periphyton colonization in both the control and atrazine limnocorrals.